I like to drink tea, especially love Pu'er tea. I read Fang Zhouzi's popular science article not long ago. It states that avoiding drinking tea produced carcinogenic aflatoxin can prevent cancer or carcinogenicity. This article quotes two scientific papers from previous years. In 2010, researchers at the Guangzhou Center for Disease Control and Prevention examined 70 samples of Pu'er tea in the Guangzhou market and found that all of them can detect aflatoxin. In 2012, a student from Nanchang University collected 60 Pu'er teas from Nanchang Market, 7 of which exceeded the standard in aflatoxin. After reading this article, I couldn't help but take a deep breath, turned around and brewed a cup of Pu'er tea to clam.
Holding a cup of tea, I began to think that if Pu'er tea contains a variety of mycotoxins as described in the two scientific papers and the concentration of aflatoxin is greatly exceeded, aflatoxin is a carcinogenic chemical, especially B1 in Pu'er tea. It is a great threat to people health. Lifestyle can change the epidemiological results of Chinese cancer. Epidemiological knowledge shows that the contamination rate of aflatoxin in food is positively correlated with the mortality rate of liver cancer in the region. In China, the lowest mortality rate of liver cancer is in Yunnan province (the origin of Pu'er tea). From the relation mentioned above, it seems that it does not support the hypothesis that Pu'er tea is carcinogenic.
The questions raised in the article are still very important and deserve to be studied carefully. In addition to these two papers, there are many articles on the detection of mycotoxin in Pu'er tea, but the results are inconsistent from no, micro to a lot. From these results, it is speculated that the Aspergillus flavus in Pu'er tea may come from pollution in transportation and storage, and it is not an inevitable product in the fermentation process. And the pollution of the product will make results tend to be consistent in the detection. If it is not the pollution brought about by fermentation, black tea, black tea, even green tea, and coffee may be contaminated by mycotoxins from others theoretically.
I quickly checked the situation of other kinds of tea on the Internet. And I quickly found that mycotoxin was detected in different kinds of tea and coffee. One of the articles on the internet(Emilia Ferrer et al., Simultaneous determination of mycotoxin in commercial coffee, Food Control 2015, 57: 282-292) reported that researchers used mass spectrometry to analyze 100 samples of coffee sold in Spanish supermarkets. A variety of mycotoxins were detected, including fumonisins, aflatoxins, trichothecenes, and emerging mycotoxins (concentrations ranging from 0.10 to 3.570 μg / kg). They also found that ochratoxin A in five samples of coffee exceeded the maximum allowable level currently.
Experiment to verify the content of aflatoxin in Pu'er tea
I made a few assumptions and it needs to be proven by analyzing a batch of tea independently in the lab. Firstly, the productive process of Pu'er tea will not produce aflatoxin and other mycotoxins. These kinds of fungi contained in tea come from pollution during subsequent transportation and storage, so we simultaneously test Pu'er tea, green tea, and black tea. The sample should get similar results. Some people have done a simulation experiment of Pu'er tea in pile fermentation and inoculated Aspergillus flavus(a kind of fungus) into three groups of Yunnan raw tea with big leaf. The results are very interesting. The content of aflatoxin in peanut in the control group reached the highest peak at 12,173μg /kg on the 20th day. A small amount of aflatoxin (1.05 μg/kg) was detected in sterilized group A, and the content of aflatoxin was lower than the hygienic standard, while the unsterilized group B and the untreated group C did not detect Aspergillus flavus. This experiment may need to be repeated furtherly. Does the result suggest that Aspergillus flavus is not suitable for growth in the micro-ecology of fermentation in Pu'er tea?
Secondly, laboratory pollution problems may be the main cause of inconsistent test results. Since there are microfungi in tea, why is it not exist in the laboratory? Common parasitic molds are widely found in warm areas at temperatures of 25-40°C, so laboratories located in tropical areas or under normal temperature conditions tend to contamination. Today's laboratories use triple quadrupole tandem mass spectrometry. These highly sensitive analytical instruments will false-positive results, due to micro fungal contamination of laboratory in equipment, materials, reagents, etc. Our laboratory used the triple quadrupole mass spectrometer to start the blank test before the tea test. And it found that there are mycotoxins. This factor was removed after the instrument was cleaned and replaced with reagents.
Thirdly, the choice of method in detection is also important. We use boiling water to brew tea and drink tea soup. Compared with corn, peanuts, and other foods, there is a fundamental difference in the edible method and dosage. Aflatoxin is fat-soluble but slightly soluble in water. The ratio of dissolution in aflatoxin between hot water and an organic solvent is different. The extraction method of boiling water is used to simulate the actual situation in tea drinking (single brewing and multiple brewing in tea sampling), which should be able to detect the mycotoxin entering in the water more accurately. The extraction method of organic solvent is more suitable for detecting the content of mycotoxins in foods.
We purchased 20 kinds of teas that is available commercially from China, Taiwan, India, Japan, etc., including Chinese Pu'er tea (Pu'er in Dibo, Gonglinxiang and Nuoxiang , Chinese Tea Pu'er, Lupicia Tea, 2009 Pu'er cooked tea and 2016 Pu'er tea), Chinese green tea (Tieguanyin Zhifu, Tieguanyin Sifang, Taiwan Oriental beauty), Chinese black tea Jinjunmei, Chinese green tea (Qianzhang Baihao, West Lake Longjing), Indian black tea (Lupicia in Muscat,Nilgiri Fop，earl grey and English black tea),South African black tea(Vanilla bourbon tea), Japanese green tea (Ito green tea and Lupicia Houji tea). Using organic solvent (acetonitrile-2% formic acid water (1/1, V/V)) and 80°C hot water to extract mycotoxins from 20 tea leaves. Using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/ MS) method to analyze and investigate in methodology. And the absolute content of aflatoxins (B1, B2, G1, and G2), fungal toxin (FB1, FB2, FB3) and deoxynivalenol in each kind of tea need to be detected.
We found that the detection method using organic solvent extraction, a variety of tea products including Pu'er tea, black tea, green tea, detected a very small amount of mycotoxins, among which aflatoxin B2 was detected in 6 kinds of tea products. Aflatoxin G1 was detected in 4 kinds of tea leaves. Fumagillin FB1 was detected in 3 kinds of tea leaves. Fumagillin FB2 was detected in one kind of tea leaf. The most toxic aflatoxin B1 was not detected. In the samples extracted at 80°C hot water, except a small amount of (0.15-3.33μg/kg) of fumonisin B1 and B2 detected in Nuoxiang tea, the 8 mycotoxins in the samples were not detected in the test.
The US Food and Drug Administration and the Chinese National Standard GB2761 in "Fungaltoxin Limits in Food" stipulate that the limited standard of aflatoxin in food, corn, corn products, peanuts, and peanut products is 20 μg/kg. The limited standard of deoxynivalenol is 1,000 μg / kg in corn, cornmeal, barley, and wheat. The international limited standard for fumonisin is not more than 1,000 μg / kg in corn and corn products. The content of mycotoxin in tea detected by our two extraction methods was between 0.15 and 7.41 μg/kg, which did not exceed the limit of mycotoxin in international food safety regulations.
To sum up, we have randomly sampled the results in 20 kinds of commercially available teas. Several Pu'er tea products contain mycotoxins including aflatoxin, but it is below the limit of standard value. The mycotoxin contained in Pu'er tea products is not significantly higher than other kinds of tea (black tea, green tea, etc,.). With the extraction test of hot water, the amount of micro mycotoxins contained in the tea leaves is quite little.
Due to the limited quantity in the sample, these test results do not cover other Pu'er tea on the market. The food safety of various tea drinks (composed of potential toxins such as pesticides, heavy metals, and fungal metabolites) is always a major issue in public. To solve such problems fundamentally, we need to develop a set of scientific and effective hygiene standards for these products. Those who are interested in reading our specific methods of testing results can download the literature online. As stated in the article, we hope that this work will provide some basis for preliminary research and technology for future development in implementing hygiene standards, including toxins in tea.